Sound-damping air-conducting duct and method for the production of a sound-damping air-conducting duct

ABSTRACT

A sound-damping air-conducting duct that has at least one exit opening for air, and is provided, in the region of the exit opening, with a lining made of a sound-absorbing material, which lining is surrounded, at least on its outside, by a wall made of plastic, provided with holes, and the lining is attached to this wall, whereby the lining is immediately, preferably directly, connected with the wall, with material fit and/or shape fit, and/or is connected with it in a single work step with the wall that is produced using a primary shaping method. A method for the production of a sound-absorbing air-conducting duct is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of German Application No. 10 2007 060 525.2 filed Dec. 13, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sound-damping air-conducting duct or to an air-conducting duct for air conditioning and/or ventilation systems, particularly for vehicles or in a vehicle, preferably for motor vehicles or in a motor vehicle. The duct has at least one exit opening for air, and is provided, in the region of the exit opening or in the exit region, preferably by way of a longitudinal segment, with an at least partially air-permeable or sound-permeable lining made of a material that absorbs or damps sound carried in the air, which lining is surrounded, at least on its outside, by a wall made of plastic, provided with holes at least in the region of the lining, preferably forming a self-supporting line segment, and the lining is attached to this wall.

2. The Prior Art

A sound-damping device for ducts of or in air-conditioning systems and the like, through which air flows, or which conduct air, has become known from DE 82 15 489 U1.

In the case of this sound-damping device, a sound-absorbing or sound-damping lining, which preferably consists of a foam material web that has a skin on at least one side, but can also consist of a non-woven fabric or another sound-absorbing material, can be surrounded, on the outside, by a carrier that can consist of a perforated, hard material, for example of plastic, and supports the lining and forms a self-supporting line segment of the air duct.

This sound-absorbing lining can achieve a significant reduction in the noise level by damping the reflected sound waves in the exit region of the air duct. The lining is sound-permeable at least in part, so that sound waves can pass through the lining and also through the holes of the carrier, without being disruptive in the space to be air-conditioned, into which the air is passed from the exit opening of the air duct.

For the production of this line segment, it is provided to pre-finish the stiff, perforated carrier, and then to apply the foam material lining.

It has also become generally known to produce similar molded parts that absorb sound carried in air, specifically by means of multi-step methods, which comprise deforming, cutting to size, and coating with adhesive, lamination or welding, and subsequent processing.

Such production is complicated and expensive. In addition, detachments of the lining can occur, which can then get into the space to be ventilated or air-conditioned, and consequently into the air that is being breathed in, so that they represent a hazard for life and health.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a sound-damping air-conducting duct that can be produced in more cost-advantageous manner, while providing advantageous possibilities for further improved noise reduction, and in which detachments of the sound-absorbing lining are avoided or prevented.

These and other objects are achieved, according to the invention, by means of a ventilation duct having the characteristics mentioned initially, particularly in that the lining is immediately connected with the wall, with material fit and/or shape fit, i.e. without any separate connection and adhesion agents, such as glues, preferably directly, or without any intermediate layer or without multiple intermediate layers, particularly without welding, and/or is connected with the wall in a single work step with the wall that is produced using a primary shaping method.

By means of these measures, particularly cost-advantageous production can be achieved, and the sound-absorbing lining remains securely connected with the wall of the sound-damping and air-conducting duct even over an extended period of time. By means of a suitable layout of the holes of the wall in combination with a thin lining, it is made possible that noises or sound waves that are provoked by a fan wheel or the like, or by air that flows in the shafts of an air-conditioning system, can flow through the holes of the wall into a cavity, or can be deflected, without being disruptive in the space to be ventilated or air-conditioned. At the same time, the air flow can flow through the ventilation channel, and exit from its exit opening, essentially free of losses, i.e. at a low flow resistance.

According to an advantageous embodiment, it can be provided that the lining has a profiled surface and/or one provided with nubs, on its inside and/or outside. In this way, the sound-absorbing effect can be further reinforced and/or in this way, better adhesion or fixation of the lining to the wall can be achieved.

Furthermore, it can be provided that the lining is configured to be porous and/or open-celled, at least on its outside, in such a manner that the thermoplastic plastic of the wall passes through the lining, at least in partial regions or in part. In this way, an even better connection of the lining to the wall, secure against detachments, can be achieved.

Furthermore, it can be provided that the lining is not completely infiltrated or penetrated by the thermoplastic plastic of the wall, so that the inner surface or inside of the lining is essentially free or completely free of the thermoplastic plastic of the wall. In this way, it can be assured that the air flow through the air-conducting duct remains essentially uninfluenced by the lining in the region of the lining, and consequently can be conducted to the outside through the exit opening with little flow resistance and minimal noise development.

Furthermore, the thermoplastic plastic of the wall can engage behind internal material structures, for example fibers, of the lining. By these measures, further improved adhesion and shape-fit attachment of the lining to the wall, and consequently even greater security against detachment of the lining, can be achieved.

In a particularly advantageous embodiment, it can furthermore be provided that the lining has a thickness that is less than 1.0 mm, preferably approximately 0.5 mm.

In a particularly preferred embodiment, it can be provided that the lining is compressed to a thickness that amounts to a fraction of its original thickness, and that is less than 1.0 mm, preferably approximately 0.5 mm.

Furthermore, it can advantageously be provided that the holes pass completely through the wall, in other words are structured as passage holes. In this way, disruptive noises can be conducted away in particularly advantageous manner.

According to a particularly preferred embodiment, it can furthermore be provided, particularly in combination with the above measures relating to the thickness of the lining, in particularly advantageous manner, that the holes of the wall have a diameter, preferably an average diameter, of 1 to 3 mm, preferably of 1.5 to 2.5 mm, particularly of 1.8 to 2.2 mm. By means of these measures, specifically by means of a lining compressed to a thickness of only approximately 0.5 mm, which is configured with or is preferably a non-woven fabric that can have a weight per surface area of about 200 g/m , in combination with opening or hole diameters of 1.8 to 2 mm, increased or maximized sound damping results in that noises or sound waves penetrate through the holes and can be conducted away. Furthermore, the use of such a thin, preferably planar lining, particularly in the form of a non-woven fabric, makes it possible that no or no noteworthy moisture can collect in it.

Furthermore, it can be practical that the holes of the wall are structured conically. Alternatively or additionally, it can be provided that at least the holes in the wall provided in the region of the lining narrow in cross-section, preferably continuously, towards the lining. In this way, problem-free and cost-advantageous production is made possible, with advantageous sound and noise absorption.

Furthermore, it can be provided that the holes of the wall provided in the region of the lining, preferably all of them, are covered by the lining, preferably completely, in each instance, and preferably are immediately delimited by the lining. In this way, particularly great sound damping or sound absorption can be achieved, at comparatively simple producibility.

In another aspect, the above object is also achieved by a method for the production of a noise-damping air-conducting duct or an air-conducting duct that absorbs sound carried in air, for air conditioning and/or ventilation systems, particularly for vehicles, preferably motor vehicles. To the extent possible, the duct preferably has the characteristics indicated above, individually or in any desired combination, and/or the characteristics as discussed herein and contains at least one exit opening for air, and is provided, in the region of the. exit opening or in the exit region, preferably by way of a longitudinal segment, with an at least partially air-permeable or sound-permeable lining made of a material that absorbs or damps sound carried in the air, preferably formed with a or from a non-woven fabric. The lining is surrounded, at least on its outside, by a wall made of plastic, provided with holes, at least in the region of the lining, preferably forming a self-supporting line segment, and the lining is attached to this wall. According to the invention, the wall is produced from a thermoplastic plastic, using a primary shaping method, preferably using an injection-molding and/or transfer-molding method and/or impact-extrusion method, and the lining is connected with the wall in a work step during or upon formation or shaping of the wall, preferably immediately, i.e. without any separate connection or adhesion means, such as glues, for example, preferably directly, i.e. without an intermediate layer or without multiple intermediate layers, particularly without welding, preferably with material fit and/or shape fit.

In this manner, the separate handling of the linings and the walls of the air-conducting ducts to be connected with them, which was previously necessary, is eliminated. Furthermore, by means of the production in one work step, in comparison with the previous production of the wall in a separate work step, and its subsequent connection with the lining in two separate work steps, significant time, effort, and costs are saved. Furthermore, additional measures for attaching the lining to the wall, as they were previously necessary, for example by means of lamination, particularly by means of gluing, are eliminated. Furthermore, as a result, particularly advantageous connection conditions between the lining and the wall are made possible, so that the risk of detachments of the wall can be minimized or even entirely precluded. In this manner, the lining or the acoustically active region formed by the lining becomes an integral component of the air-conducting duct. No further components to be handled separately or produced in separate work steps, and to be connected, such as separate sound-absorbing material or plates within the duct, or outside walls, such as in exhaust gas mufflers, are necessary.

It is particularly advantageous if the lining is compressed to a fraction of its original thickness before and/or during the formation or shaping of the wall, at least in partial regions.

Furthermore, it can be provided that the lining is mechanically compressed by means of mechanical forces of die structures that determine the configuration and/or the shape of the holes of the wall, for example of pins that form hole cores and the like, a mold die, at local pressure points. Alternatively or additionally, it can be provided that the lining is compressed upon or during the formation or shaping of the wall, at least in partial regions, by means of the internal pressure forces exerted by the molten or viscous thermoplastic plastic material.

According to a particularly preferred embodiment, in a first step, the lining is compressed by mechanical forces of die structures that determine the configuration and/or the shape of the holes of the wall, for example by pins that form hole cores, and the like, a mold die, at local pressure points. At the same time or subsequently, the lining is compressed in regions disposed adjacent to and/or between the local pressure points, by the internal pressure forces of the molten or viscous plastic material that occur during formation or shaping of the wall.

In a particularly advantageous further development of the air-conducting duct and/or of the method for the production of the or an air-conducting duct, it can be provided that the lining is compressed before and/or during the formation or shaping of the wall, in such a manner that the holes of the wall of the finished air-conducting duct are immediately delimited, at least in part, preferably essentially, by the lining. In this way, particularly great sound damping or sound absorption can be achieved, with comparatively simple producibility.

Furthermore, the lining, in the finished, compressed state or in the finished air-conducting duct, in the region of or at the local pressure points, may have a thickness that approximately corresponds to the thickness of the lining in the regions that immediately follow the local pressure points and/or in the regions disposed adjacent to the local pressure points.

Alternatively, it can be provided that the lining, in the finished, compressed state or in the finished air-conducting duct, in the region of or at the local pressure points, has a thickness that is different as compared with the regions adjacent to the lining, particularly smaller.

In a further preferred embodiment of the method, this can be characterized by the following steps:

a) The lining is introduced into an open mold die, which has a die core; b) the lining is held on or on top of the die core, to prevent detachment from the and/or displacement relative to the die core, by means of at least one holding and/or fixation means; c) the plastic material for the wall

-   -   is introduced into the open mold die, which is subsequently         closed, whereby and/or whereupon the wall is formed and         connected with the lining, in one work step, and/or     -   is injected and/or pressed into the closed mold die, whereby         and/or whereupon the wall is formed and connected with the         lining, in one work step.

For holding or fixing the lining on or on top of the die core, the die core can be provided with bores that open on the side of the die core that lies opposite the lining, and at which a partial vacuum or vacuum can be applied, in controlled or regulated manner. In this way, the lining can be held on or on top of the die core, secured relative to the die core, to prevent detachment and/or displacement, particularly due to internal pressure forces that occur during the formation or shaping of the wall. After the wall has been completely formed or shaped, and firmly connected with the lining, the partial vacuum or the vacuum can be taken away. In this way, the finished molded part can subsequently be removed from the mold die.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present inventions will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the inventions.

In the drawings, wherein similar reference characters denote similar elements throughout the several views:

FIG. 1 is a longitudinal cross-section of an air-conducting duct according to an embodiment of the invention;

FIG. 2 is an enlarged cross-section of the air-conducting duct along the section lines A-A in FIG. 1, in the region of a sound-absorbing lining;

FIG. 3 shows a mold die for the production of an air-conducting duct according to the invention, having a die core on which a lining is disposed and held, whereby the die is in a state in which it is not yet completely closed;

FIG. 4 is an enlarged view of a section of the mold die for the production of an air-conducting duct according to the invention, whereby pins or core disposed at a distance from one another are provided on a first die half, which determine the holes to be provided in the wall of the air-conducting duct, whereby the die is now shown in a closed state, in which the lining disposed on the die core is mechanically compressed by means of the pins or cores, at local pressure points, and whereby there is not yet any plastic material for the formation or shaping of the wall of the air-conducting duct situated in the region between the pins or cores.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in detail to the drawings, the air-conducting duct 20 shown schematically in longitudinal cross-section in FIG. 1 is configured in tubular shape and has an entry opening 21 for air and an exit opening 22 for the air that flows through air-conducting duct 20 in the direction of the arrow 51. Entry opening 21 can stand in a flow connection with an air transport device, not shown in the figures, for example with a fan and/or with an air-conditioning system for conditioning the air. The air to be conveyed in air-conducting duct 20 in direction 51, if applicable air-conditioned air, can be transferred to a space or chamber 50 to be ventilated or to be air-conditioned, out of exit opening 22. In a region ahead of exit opening 22, air-conducting duct 20 widens up to exit opening 22, so that the cross-sectional shape changes in this duct segment region, in the longitudinal direction of air-conducting duct 20; here, it widens crosswise or perpendicular to direction 51.

In this widening end or exit region 23 of air-conducting duct 20, a lining or inlay 25 is disposed, here in the form of a non-woven fabric, preferably having a weight per surface area of about 200 g/m². Lining 25 is immediately connected with the wall 31 of air-conducting duct 20, with material fit and/or shape fit, i.e. without any separate connection and/or adhesion agents, such as glues, directly, i.e. without one or more intermediate layers, and is connected with wall 31 in a single work step with wall 31 of air-conducting duct 20 produced using a primary shaping method. Lining 25 consists of sound-absorbing material. It is surrounded, at least on its outside 26, by a wall 31, and attached to wall 31. Wall 31 is provided with holes, here passage holes 30, at least in the region of lining 25, and forms a self-supporting line segment here. Wall 31 consists of a thermoplastic plastic or is formed from a thermoplastic plastic. In other words, it can also have fillers and/or reinforcement substances. The plastic can preferably be polypropylene.

Lining 25 extends over a longitudinal segment 24 of the air-conducting duct 20, which here is essentially delimited with or by the end region of air-conducting duct 20, which widens outward. In the region of lining 25, air-conducting duct 20 has an acoustically optimized region 29. The inside 27 or the inner surface 28 of lining 25 is preferably disposed in such a manner that it aligns with the subsequent wall parts of wall 31 of air-conducting duct 20, so that in the transition region from wall 31 to lining 25, in each instance, essentially no flow losses or disruptive noises occur.

In the region of lining 25, a collection chamber 49 is provided on the outside of air-conducting duct 20, into which part of the sound waves or noises can be passed in the direction of arrows 52, which can be caused, for example, by a fan or an air-conditioning system or the like. For this purpose, the lining is surrounded on its outside 26 by a wall 31 of air-conducting duct 20 that functions as a carrier for lining 25, which wall supports the sound-absorbing lining and on which the lining is attached, secured to prevent detachment.

Wall 31 of air-conducting duct 20 consists of a comparatively hard, self-supporting plastic, preferably of polypropylene. In the region of lining 25, wall 31 has a plurality of holes 30, which are spaced apart, preferably at regular intervals. Holes 30 pass through wall 31 completely, in other words are configured as passage holes. In the region of lining 25, holes 30 are covered completely by lining 25, in each instance, towards the inside. Holes 30 are preferably configured conically. In other words the holes preferably have a trapezoid cross-section, whereby the cross-section of holes 30 narrows towards lining 25, preferably continuously. It is understood that instead of conical holes, other hole cross-sections, for example cylindrical holes or holes having a different cross-section, can also be provided.

In the exemplary embodiment shown, lining 25 consists of a non-woven fabric that is formed from fiber-shaped structures. The non-woven fabric is at least partially air-permeable or noise-permeable, and is configured with relatively porous or loose fiber structures. Non-woven fabric 25 is infiltrated, from its outside 26, by the thermoplastic plastic of wall 31, at least in part, but not completely to inside 27 or inner surface 28 of lining 25. Consequently, inside 27 or inner surface 28 of lining 25 is entirely or essentially free of the thermoplastic plastic of wall 31 that supports lining 25.

The fibers of the lining or of non-woven fabric 25 form internal material structures behind which the thermoplastic plastic of wall 31 engages, at least in part, so that lining 25 is immediately and directly connected with wall 31 or with the thermoplastic plastic of wall 31, with shape fit. Depending on the lining material that is used, particularly the fiber materials of the non-woven fabric, a material-fit connection between wall 31 or the thermoplastic plastic of wall 31 and lining 25 can also preferably take place.

Holes 30 of wall 31 that are provided in the region of lining 25 have a diameter or average diameter 32 that amounts to about 1.8 to 2.2 mm here. The lining or non-woven fabric 25 has a thickness 35, 36 that remains essentially the same in the entire acoustically optimized region 29, of less than 1.0 mm. Preferably, the thickness 35, 36 amounts to approximately 0.5 mm. Lining 25 is compressed to a fraction of its original thickness 34 in the acoustically optimized region 29, specifically to the thickness 35, 36. In this way, no or essentially no moisture can collect in the non-woven fabric. Despite the comparatively very thin non-woven fabric, excellent noise damping can be achieved, surprisingly, specifically in combination with diameters 32 of holes 30 of wall 31 that are dimensioned in a range of 1.8 to 2.2 mm, whereby the air flow can flow through air-conducting duct 20 and out of exit opening 22, uninfluenced or essentially uninfluenced, in loss-free or essentially loss-free manner.

Air-conducting duct 20 can be produced, according to the invention, in that wall 31 that surrounds and supports the lining, here non-woven fabric 25, is produced from a thermoplastic plastic, using a primary shaping method, preferably using the injection-molding method, whereby the wall can alternatively or additionally be produced using the transfer-molding method and/or using the impact-extrusion method. Furthermore, lining 25 is connected with wall 31, according to the invention, in a work step during or upon formation or shaping of wall 31, preferably immediately, i.e. without any separate connection or adhesion means, such as glues, for example, preferably directly, i.e. without one or more intermediate layers, preferably with material fit and/or shape fit.

The production of air-conducting duct 20 using a preferred injection-molding method is described in greater detail in the following:

FIG. 3 shows, in a schematic representation, a mold die 40, which here has a first or upper die half 41 and a second or lower die half 42, as well as a central die core 44. Lining 25 is disposed on die core 44 as an insertion part, and is held there secured to prevent detachment from and/or displacement relative to die core 44. For this purpose, holding and/or fixation means that are not shown in the figures can be provided. Such holding means can be configured with bores, for example, which are provided in die core 44. These bores can open towards the die cavity or towards the cavity 45. In other words the bores can open towards inside 27 or inner surface 28 of lining 25. A partial vacuum or vacuum can be applied at the bores, in controlled or regulated manner, thereby causing lining 25 to be drawn against die core 44 and held in place there.

The first, here upper die half 41, is provided with a plurality of conical pins that narrow towards their free end, which are spaced apart, preferably at the same or regular intervals, which pins are also referred to as die structures 43 and which form cores for holes 30 to be provided in wall 31 to be formed. These die structures 43 determine the configuration and shape of holes 30 of wall 31.

In FIG. 3, mold die 40 is shown in a position in which it is not yet completely closed. In this position, the first, here upper die half 41, is disposed at a distance from die core 44, in such a manner that the free ends of pins 43 just rest against outside 26 of lining 25, which has a specific original thickness 34. This starting thickness 34 of lining 25 amounts to about 2 to 3 mm here. It is also possible to use a very much thicker starting material, 1 to 30 mm, or even more, for the lining. The starting material or the lining does not have to be a finished non-woven fabric raw material; it can also be an unfinished non-woven material that has a cotton-like state, particularly, in other words, is not needled or consolidated by means of binders.

Proceeding from the position shown in FIG. 3, mold die 40 is completely closed, whereby or whereupon molten or viscous thermoplastic plastic can be injected, under pressure, through the feed channel or sprue 46 provided in first die half 41 here, for the purpose of forming and shaping wall 31, and more pressure can be applied, if necessary.

In the completely closed state of mold die 40, pins or cores 43 are in a position relative to die core 44 as is evident from FIG. 4. In this position, lining 25 has been mechanically compressed by pins or cores 43, at local pressure points 33, to a thickness 35 that amounts to only a fraction of its original thickness 34.

In other words, lining 25, proceeding from the open position of mold die 40 shown in FIG. 3, and proceeding from its original thickness 34, is mechanically compressed, in the course of subsequent closing of mold die 40, by pins or cores 43, in the region of their free ends, to a thickness 35 that amounts to only a fraction of this original thickness 34, whereby local pressure points 33 are formed. The thickness 35 of the compressed lining 25 in the region of the local pressure points 33 preferably amounts to about 0.5 mm.

Subsequently, in other words after complete closing of die 40, but possibly also at a point in time at which mold die 40 is not yet completely closed, molten or viscous thermoplastic plastic is injected into die cavity 45 or into the cavity of mold die 40, by way of feed channel or sprue 46, whereby the material flows around the pins or cores. In the course of injection or transfer of molten or viscous thermoplastic plastic, which takes place under elevated hydraulic pressures, internal pressures occur in cavity 45, by means of which lining 25 is compressed, proceeding from its original thickness 34, to a fraction of this original thickness 34, also in regions. formed adjacent to and between the local pressure points 33. Preferably, the lining is compressed, also in these additional or other regions, to a thickness 36 that approximately corresponds to the thickness 35 of lining 25 mechanically compressed by pins or cores 34. In this way, a finished component is obtained, which is shown in cross-section in FIG. 2, and in which lining 25 has an approximately uniform thickness 35, 36 in the acoustically optimized region 29.

In the case of the method according to the invention, the internal pressure forces that act on lining 25 by means of the molten or viscous thermoplastic plastic material during the formation or shaping of wall 31, act on it essentially only by way of its outside 26. In the exemplary embodiment, these internal pressure forces also act on lining 25 by way of its edge or face surfaces, but not by way of inside 27 of lining 25 that lies against die core 44.

Accordingly, although only a few embodiments of the present invention have been shown and described, it will be apparent that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 

1. A sound-damping air-conducting duct for an air conditioning or ventilation system comprising: (a) at least one exit opening for air; (b) a lining made of a sound-absorbing material provided near said at least one exit opening, said lining having an outside portion; (c) a wall made of plastic attached to said lining and surrounding at least an outside portion of said lining, said wall being provided with a plurality of holes at least near said lining; wherein said lining is immediately connected with the wall with a material fit or shape fit or is connected with the wall in a single work step when the wall is formed.
 2. The sound-damping air-conducting duct according to claim 1, wherein the air conditioning or ventilation system is in a vehicle, said lining comprises a non-woven fabric, said wall forms a self-supporting line segment, and said lining is directly connected with the wall.
 3. The sound-damping air-conducting duct according to claim 1, wherein the lining has a profiled surface or a surface provided with nubs on an inside portion of said lining or on the outside portion.
 4. The sound-damping air-conducting duct according to claim 1, wherein the plastic is a thermoplastic plastic and the lining is porous or open-celled at least on the outside portion such that the thermoplastic plastic of the wall passes through the lining at least in partial regions of the lining or at least in part.
 5. The sound-damping air-conducting duct according to claim 4, wherein the lining is not completely infiltrated or penetrated by the thermoplastic plastic of the wall so that the surface of an inside portion of the lining is essentially free or completely free of the thermoplastic plastic of the wall.
 6. The sound-damping air-conducting duct according to claim 4, wherein the lining comprises internal material structures and the thermoplastic plastic of the wall engages behind said internal material structures.
 7. The sound-damping air-conducting duct according to claim 6, wherein the internal material structures comprise fibers.
 8. The sound-damping air-conducting duct according to claim 1, wherein the lining has a thickness that is less than 1.0 mm.
 9. The sound-damping air-conducting duct according to claim 1, wherein the lining has a thickness of approximately 0.5 mm.
 10. The sound-damping air-conducting duct according to claim 1, wherein the lining has an original thickness and the lining is compressed to a compressed thickness that amounts to only a fraction of the original thickness.
 11. The sound-damping air-conducting duct according to claim 1, wherein the holes of the wall comprise passage holes.
 12. The sound-damping air-conducting duct according to claim 1, wherein the holes of the wall have an average diameter or a minimal diameter of 1 to 3 mm.
 13. The sound-damping air-conducting duct according to claim 1, wherein the holes have an average diameter or a minimal diameter of 1.5 to 2.5 mm.
 14. The sound-damping air-conducting duct according to claim 1, wherein the holes have an average diameter or a minimal diameter of 1.8 to 2.2 mm.
 15. The sound-damping air-conducting duct according to claim 1, wherein the holes of the wall are conical.
 16. The sound-damping air-conducting duct according to claim 1, wherein at least the holes of the wall provided near the lining narrow in cross-section towards the lining.
 17. The sound-damping air-conducting duct according to claim 16, wherein the holes narrow continuously toward the lining.
 18. The sound-damping air-conducting duct according to claim 1, wherein the holes of the wall provided near the lining are covered by the lining.
 19. The sound-damping air-conducting duct according to claim 18, wherein the holes are immediately delimited by the lining.
 20. A method for producing a sound-damping air conducting duct for air conditioning or ventilation system comprising the steps of: (a) producing a wall from thermoplastic using a primary shaping method selected from the group consisting of an injection-molding method, a transfer-molding method, and an impact-extrusion method; and (b) connecting a lining made of sound-absorbing material with the wall in one work step during formation or shaping of the wall; wherein the duct has at least one exit opening for air and is provided with the lining; wherein the lining is surrounded at least on an outside portion of the lining by the wall; and wherein the wall is provided with holes.
 21. The method accordingly to claim 20, wherein the lining is immediately connected with the wall with a material fit or a shape-fit; the air conditioning or ventilation system is in a vehicle; the lining comprises a non-woven fabric; and the wall forms a self-supporting line segment.
 22. The method according to claim 21, wherein the vehicle is a motor vehicle and the lining is directly connected with the wall.
 23. The method according to claim 20, wherein the lining has an original thickness and the lining is compressed to a fraction of the original thickness before or during the formation or shaping of the wall, at least in partial regions of the lining.
 24. The method according to claim 20, wherein the lining is compressed by mechanical forces of die structures of a mold die that determine configuration or shape of the holes of the wall at local pressure points.
 25. The method according to claim 20, wherein during the formation or shaping of the wall, the thermoplastic plastic is provided in a molten or viscous state and the lining is compressed during the formation or shaping of the wall, at least in partial regions by the internal pressure forces exerted by the thermoplastic plastic in the molten or viscous state.
 26. The method according to claim 20, wherein during the formation or shaping of the wall, the thermoplastic plastic is provided in a molten or viscous state and the lining is compressed by mechanical forces of die structures of a mold die that determine the configuration or the shape of the holes of the wall, at local pressure points and, at the same time or subsequently, in regions disposed adjacent to or between the local pressure points by internal pressure forces of the thermoplastic plastic in the molten or viscous state that occur during formation or shaping of the wall.
 27. The method according to claim 20, wherein the lining is compressed before or during the formation or shaping of the wall, in such a manner that the holes of the wall of the sound-damping air-conducting duct in a finished condition are immediately delimited, at least in part by the lining.
 28. The method according to claim 27, wherein the holes of the wall of the sound-damping air conditioning duct in the finished condition are immediately delimited essentially by the lining.
 29. The method according to claim 24, wherein the lining in the sound-damping air-conducting duct in a finished condition, near or at the local pressure points, has a first thickness that approximately corresponds to a second thickness of the lining in regions that immediately follow the local pressure points or in regions disposed adjacent to or between the local pressure points.
 30. The method according to claim 26, wherein the lining in the sound-damping air-conducting duct in a finished condition, near or at the local pressure points, has a first thickness that approximately corresponds to a second thickness of the lining in regions that immediately follow the local pressure points or in regions disposed adjacent to or between the local pressure points.
 31. The method according to claim 24, wherein the lining, in the sound-damping air-conducting duct in a finished condition, near or at the local pressure points, has a thickness that is different as compared with adjacent regions of the lining.
 32. The method according to claim 26, wherein the lining, in the sound-damping air-conducting duct in a finished condition, near or at the local pressure points, has a thickness that is different as compared with adjacent regions of the lining.
 33. The method according to claim 31, wherein the thickness is smaller as compared with the regions adjacent to the lining.
 34. The method according to claim 32, wherein the thickness is smaller as compared with the regions adjacent to the lining.
 35. The method according to claim 20, wherein: (a) the lining is introduced into an open mold die having a die core; (b) the lining is held on or on top of the die core, to prevent detachment from the die core or to prevent displacement relative to the die core by at least one holding or fixation device; and (c) the plastic material for the wall is introduced into the open mold die, the open mold die is subsequently closed, whereby or whereupon the wall is formed and connected with the lining in one work step, or the open mold die is closed and the plastic material for the wall is injected or pressed into the closed mold die, whereby or whereupon the wall is formed and connected with the lining, in one work step. 